Numerous systems have previously been proposed to allow weapon platform operators to determine whether a potential target is friendly or unfriendly. In general, such systems have used electromagnetic means, such as radio and radar, which have several practical disadvantages. For one, electromagnetic radiation spreads over a wide area and makes correlation of specific targets in a group of targets difficult. For another, electromagnetic radiation is subject to jamming and interference. Finally, electromagnetic radiation can be detected from many directions, and thereby gives away the location of the weapon platform.
For all of the foregoing reasons, it has been the custom in practice to use visual identification whenever practical. Because line-of-sight observation is often limited by atmospheric conditions, however, the visual identification approach unnecessarily reduced the effectiveness of the weapon platform.
The prior art includes the following references: U.S. Pat. No. 4,014,482 which shows a beam rider guidance system; U.S. Pat. No. 4,164,165 which shows a firing safety system inhibiting fire in unsafe directions; U.S. Pat. No. 4,234,141 which allows a beam rider system in which missile position information is reflected back to the launch site; U.S. Pat. No. 4,406,429 which shows a system for tracking, by means of a night sight, a missile carrying an IR transmitter; U.S. Pat. No. 4,424,943 which shows a missile identification and tracking system involving a missile-mounted pulsed laser in addition to IR; U.S. Pat. No. 4,464,974 which involves laser tracking and guidance of a simulated missile; and German published application 3,150,173 which describes a missile-mounted IFF system for interrogating a target upon approach thereto, and disarming the missile if the target responds with a predetermined code.